" At The Rockefeller University, there are three relatively large, highly successful and productive structural biology groups that use X-ray crystallography as a major tool (Darst, structural biology of bacterial transcription; MacKinnon, structural biology of ion channels; Stebbins, structural biology of bacterial pathogenesis). In the last 5 years or so, three additional groups at Rockefeller have developed significant X-ray crystallography programs (Blobel, mRNA nuclear export; Rice, viral replication; Sakmar, G protein-coupled signalling). These efforts began as formal or informal collaborations with the structural biologists at Rockefeller, but in each case success has led to the expansion of these efforts, such that these groups support X-ray crystallography programs as large and active as the structural biologists. This situation has led to a need for significant upgrades of the in-house X-ray equipment at The Rockefeller University. Specifically, this Shared Instrumentation Grant proposes the following upgrades: 1) An R-Axis IV++ area detector to replace a 12-year-old R-Axis II area detector that will no longer be supported by MSC; 2) Inverse <)> brackets to add to two ports of the X-ray generator; 3) Two VariMax Cu HR confocal Max-Flux optical systems, the most advanced X-ray optics system available from Rigaku/MSC, to replace 12-year-old MSC/Yale mirrors; 4) Two X-stream cryogenic systems to replace obsolete, 15-year-old MSC cryosystems that are out of repair. These upgrades will significantly enhance the use of the machine for screening weakly diffracting crystals of membrane proteins and large macromolecular complexes, enhance data quality and throughput, as well as greatly facilitate its use for the screening and preparation of cryo-preserved crystals for synchrotron trips, which is the main use of the machines for a number of NIH-supported projects. [unreadable] [unreadable]